Mark Clarke's blog

Family converts to Linux

A few months ago I setup a new computer for my 73 year Mother and instead of installing Windows I decided to put Linux on the box. I wrestled with doing this for a while as I didn't want to have my Mom getting confused with a new interface. Previously windows had been installed on the old box. Another factor was that I am in Johannesburg while my Mom and Dad are in Durban.

Why Postfix may suddenly stop delivering mail if you using amavisd on centos 4

Today we experienced some mail delivery problems on one of our client's servers running Centos 4 and postfix with amavisd for virus and spam scanning.

Trawl the log files

The mail logs where filling with errors such as:

(delivery temporarily suspended: lost connection with[] while sending RCPT TO)

Google Web Toolkit and Echo Framework

Recently I have begun to experiment with the Google Web Toolkit. The GWT is an amazing framework that allows one to programme in pure java with the resulting application being cross-compiled into Javascript so that the entire application runs on the client browser with trips to the server occurring only when some middleware interaction takes place. Essentially your application becomes one javascript file.

Cannot find the declaration of element 'persistence'

A common error when using EJB3 is

Cannot find the declaration of element 'persistence'

This is caused by a missing xml namespace attribute declaration in your persistence.xml file. To fix this error make sure your persistence tag has the following syntax:

<persistence xmlns="" version="1.0">

instead of


Stop spam with a combined approach

Spam is the ban of any system administrators life and many people have taken it for granted that they must simply live with a certain level of spam in their day-to-day lives. However this does not have to be the case. A combined spam filtering approach is what is needed to end the spam problem. We find that a combination of blacklists and greylisting is the magic bullet that kills spam dead.


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